A reference voltage circuit is a circuit that produces a fixed voltage to a device. The fixed voltage is substantially constant despite variations in temperature. Conventional bandgap reference voltage circuits use a combination of a bipolar (or diode) base-emitter junction voltage (Vbe) and a proportional to absolute temperature (PTAT) voltage. Vbe is roughly 650 mV at room temperature and has a negative temperature coefficient (TC). The PTAT voltage has a positive TC which, when added to the negative TC of the Vbe, creates a low temperature coefficient reference voltage of about 1.24 volts.
When fabricating voltage reference circuits in integrated circuits, pressure from the package on the integrated circuit die can alter the fixed voltage produced by a voltage reference circuit. One way to avoid this problem is to use a ceramic package that can be hermetically sealed and does not induce pressure on the die. Another way to avoid this problem is to use a die coat that displaces pressure normally placed on the die. These methods can increase the production cost.